Control method of laundry machine

ABSTRACT

A control method of a laundry machine is disclosed. The control method of laundry machine having a drum, a front balancer provided with a front portion of the drum and a rear balancer provided with a rear portion of the drum includes accelerating the drum and rotating the drum at a constant speed of a predetermined rotation speed for a predetermined time period, the predetermined rotation speed allowing that perpendicular displacement at the front portion of the drum is different from that at the rear portion of the drum.

TECHNICAL FIELD

The present invention relates to a control method of a laundry machine.

BACKGROUND ART

A drum laundry machine includes a drum arranged in a horizontal direction and a drum also arranged in a horizontal direction inside the tub. Laundry is located inside the drum and is washed with tumbling in accordance with rotation of the drum.

The tub serves to receive washing water therein, and the drum serves to carry out washing of the laundry.

The drum is rotatably installed inside the tub.

A rotational shaft is connected with a rear portion of the drum, and a rotational force is forwarded from a motor to the rotational shaft. The rotational force is forwarded to the drum through the rotational shaft by rotation of the motor, whereby the drum is rotated.

The drum is rotated during rinsing and spinning cycles as well as a washing cycle. The drum is vibrated with rotating.

The rotational shaft is projected outside the tub while passing through a rear wall of the tub. In case of a laundry machine according to the related art, a bearing housing may be inserted into the rear wall of the tub by insert molding. Alternatively, the bearing housing may be fixed to the rear wall of the tub.

The rotational shaft is supported by the bearing housing, and vibration of the drum is forwarded to the bearing housing and the tub through the rotational shaft.

Accordingly, the tub is vibrated together with the drum. In order to damp such vibration, a damping support member is connected with the tub.

In other words, in the laundry machine according to the related art, vibration is forwarded to the tub, and is supported through the damping support member connected with the tub.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention is directed to a control method of a laundry machine.

An object of the present invention is to provide a control method of a laundry machine which can solve the above problem.

Solution to Problem

To solve the problems, an object of the present invention is to provide a method for passing through a transient region while reducing vibration of a drum when the drum is rotated at a speed more than the transient region in a laundry machine.

Another object of the present invention is to provide a method for controlling positions of balls of a balancer by considering characteristics of a vibration mode at a transient region.

Advantageous Effects of Invention

When a drum is rotated at a speed more than a transient region in a laundry machine, its vibration can be reduced and at the same time a rotation speed of the drum can pass through the transient region effectively.

In particular, as positions of balls of a balancer are controlled considering characteristics of a vibration mode at the transient region, unbalance is compensated to conform to the vibration mode, whereby vibration of the drum can be reduced effectively.

Moreover, vibration of the drum can be reduced effectively even in a vibration mode, i.e., a diagonal vibration mode where displacement at a front portion of the drum with respect to a rotational shaft is contrary to displacement at a rear portion of the drum.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure.

In the drawings:

FIG. 1 is a diagram illustrating a laundry machine according to one embodiment of the present invention;

FIG. 2 is a partial sectional view illustrating a laundry machine of FIG. 1;

FIG. 3 is a sectional view illustrating a front balancer;

FIG. 4 is a diagram illustrating the relation between mass and natural vibration;

FIG. 5 is a diagram illustrating the position relation between balls and unbalance based on rotation of a drum;

FIG. 6 is a diagram illustrating a spinning method according to one embodiment of the present invention;

FIG. 7 is a graph showing a relation of mass vs. a natural frequency; and

FIG. 8 is a graph illustrating vibration characteristics of the laundry machine of FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a partial exploded perspective view illustrating a laundry machine according to one embodiment of the present invention.

According to a laundry machine according to an embodiment, the tub may be fixedly supported to the cabinet or it may be supplied to the cabinet by a flexible supporting structure such as a suspension unit which will be described later. Also, the supporting of the tub may be between the supporting of the suspension unit and the completely fixed supporting.

That is, the tub may be flexibly supported by the suspension unit which will be described later or it may be complete-fixedly supported to be movable more rigidly. Although not shown in the drawings, the cabinet may not be provided unlike embodiments which will be described later. For example, in case of a built-in type laundry machine, a predetermined space in which the built-in type laundry machine will be installed may be formed by a wall structure and the like, instead of the cabinet. In other words, the built-in type laundry machine may not include a cabinet configured to define an exterior appearance thereof independently.

The laundry machine according to this embodiment of the present invention includes a tub fixedly supported to a cabinet. The tub includes a tub front 100 configured to define a front part thereof and a tub rear 120 configured to define a rear part thereof. The tub front 100 and the tub rear 120 are assembled to each other by screws and a predetermined space is formed in the assembled structure to accommodate a drum. The tub rear 120 may include an opening formed in a rear surface thereof and an inner circumference of the rear surface of the tub rear 120 is connected with an outer circumference of a rear gasket 250. An inner circumference of the rear gasket 250 is connected with a tub back 130. The tub back 130 includes a through-hole formed in a center thereof and a shaft passes the through-hole. The rear gasket 250 may be made of flexible material not to transmit the vibration of the tub back 130 to the tub rear 120.

The tub rear 120 includes a rear surface 128. The rear surface 128 of the tub rear 120, the tub back 130 and the rear gasket 250 define a rear wall of the tub. The rear gasket 250 is sealingly connected with the tub back 130 and the tub rear 120 and it prevents wash water held in the tub from leaking out. The tub back 130 is vibrated together with the drum during the rotation of the drum. At this time, the tub back 130 is spaced apart from the tub rear 120 at a predetermined distance enough not to interfere with the tub rear 120. Since the rear gasket 250 is made of a flexible material, it allows the tub back 130 to relative-move without interfering with the tub rear 120. The rear gasket 250 may include a corrugation part 252 extendible enough to allow such a relative movement of the tub back 130.

A foreign-substance-preventing member 200 is connected with a front portion of the tub front 100 to prevent foreign substances from coming between the tub and the drum. The foreign-substance-preventing member 200 is made of a flexible material and it is fixedly installed to the tub front 100. The foreign-substance-preventing member 200 may be made of the same material as that used to make the rear gasket 250 and it will be referenced to as front gasket for convenience sake.

The drum includes a drum front 300, a drum center 320 and a drum back 340. Balancers 310 and 330 are installed in front and rear portions of the drum, respectively. The drum back 340 is connected with a spider 350, and the spider 350 is connected with a rotational shaft 351. The drum 32 is rotated in the tub by the rotational force transmitted via the rotational shaft 351.

The rotational shaft 351 is directly connected with a motor by passing through the tub back 130. Specifically, the rotational shaft 351 is directly connected with a rotor of the motor. A bearing housing 400 is coupled to a rear surface of the tub back 130. The bearing housing 400 is located between the motor and the tub back 130 to rotatably support the rotational shaft 351.

A stator is fixedly installed to the bearing housing 400 and the rotor is located around the stator. As mentioned above, the rotor is directly connected with the rotational shaft 351. The motor is an outer rotor type motor and it is directly connected with the rotational shaft 351.

The bearing housing 400 is supported from a cabinet base 600 through a suspension unit. The suspension unit includes three perpendicular supporting suspensions and two oblique-supporting suspensions configured to support the bearing housing obliquely in a forward and rearward direction.

The suspension unit may include a first cylinder spring 520, a second cylinder spring 510, a third cylinder spring 500, a first cylinder damper, and a second cylinder damper 530, wherein the first cylinder damper, although not shown, is symmetrically installed to be opposite to the second cylinder damper.

The first cylinder spring 520 is connected between a first suspension bracket 450 and the cabinet base 600, and the second cylinder spring 510 is connected between a second suspension bracket 440 and the cabinet base 600.

The third cylinder spring 500 is directly connected between the bearing housing 400 and the cabinet base 600.

The first cylinder damper 540 is obliquely installed between the first suspension bracket 450 and a rear portion of the cabinet base. The second cylinder damper 530 is obliquely installed between the second suspension bracket 440 and the rear portion of the cabinet base.

The cylinder springs 520, 510 and 500 of the suspension unit may be connected to the cabinet base 600 flexibly enough to allow the drum to move in a forward-and-rearward direction and a rightward-and-leftward direction, not completely fixed to the cabinet base 600. That is, the cylinder springs 520, 510 and 500 elastically support the drum to allow the drum to rotate vertically and horizontally with respect to the connected point with the cabinet base.

The perpendicular ones of the suspensions suspend the vibration of the drum elastically and the oblique ones dampen the vibration. That is, out of the vibration system that includes springs and damping means, the perpendicularly installed ones are employed as springs and the obliquely installed ones are employed as damping means.

The tub front and the tub rear are fixedly secured to the cabinet and the vibration of the drum is suspendingly supported by the suspension unit. Substantially, the structure of the tub and the drum may be separate. Even when the drum is vibrated, the tub may not be vibrated structurally.

The bearing housing and the suspension brackets are connected by first and second weights 431 and 430.

Hereinafter, a balancer will be described in more detail.

First of all, if the drum is rotated in a state that laundry is placed in the drum, unbalance may be generated by the laundry. Since such unbalance may cause high vibration of the drum during a spinning cycle, it is preferably required to reduce such unbalance (UB). In particular, as the rotation speed of the drum is increased, it reaches a natural vibration region of the laundry machine. In this case, a problem may occur in that the vibration becomes great if unbalance is too great.

Since it is impossible to uniformly distribute the laundry inside the drum, it is important to reduce unbalance if possible. An allowable unbalance rate may be required for the laundry machine considering characteristics of the laundry machine. In this respect, it is required to sense unbalance and compare the sensed unbalance with allowable unbalance to control rotation of the drum.

In order to reduce unbalance, several solutions may be provided. One of the several solutions is laundry distribution or uniform laundry distribution for varying the position of the laundry inside the drum.

Also, in order to reduce unbalance, a fluid may be located in an opposite position of an unbalanced position of the laundry to compensate for unbalance of the laundry. In other words, a balancer may be used.

In this embodiment, a ball balancer is used as the balancer. The balancer is respectively used at the front and rear portions of the drum.

In this embodiment, as shown in FIG. 2, the front balancer 310 is provided at the front portion of the drum, and the rear balancer 330 is provided at the rear portion of the drum. In more detail, the front balancer 310 is mounted on a front surface of the drum front 300, and the rear balancer 330 is mounted on a rear surface of the drum back 340. To this end, the drum front 300 may have a front recess recessed in a rearward direction on the front surface, and the drum back 340 may have a rear recess recessed in a forward direction.

In this embodiment, although not necessarily required, it is preferably required that the front balancer 310 is structurally the same as the rear balancer 330.

FIG. 3 illustrates a sectional structure of the front balancer 310.

First of all, the front balancer 310 includes a race 31, a ball 32, and an oil 33. The race 31 may have a ring shaped ball space portion 31 a where the ball 32 can move therein. The ball space portion 31 a may have a square shape roughly as shown.

A plurality of balls 32 are received in the ball space portion 31 a. The number of balls received in the ball space portion 31 a and a diameter of the ball are defined considering the unbalance rate, together with vibration characteristics of the laundry machine.

Also, since the ball space portion 31 a is filled with the oil 33, the number and diameter of balls received in the ball space portion 31 a are preferably defined considering the amount and viscosity of the oil 33, which affect movement of the ball 32. The amount and viscosity of the oil 33 may be determined such that the ball 32 of the balancer may have required movement. Also, the amount and viscosity of the oil 33 may be determined considering vibration characteristics of the laundry machine.

In this embodiment, 14 balls 32 are received in the ball space portion 31 a, and each of the balls has a diameter of 18.55 mm to 19.55 mm, preferably 19.05 mm. The ball space portion 31 a of the race has a sectional area in the range of 410 mm ² to 413 mm ², preferably 412 mm ². A center diameter of the sectional area of the ball space portion 31 a is in the range of 500 mm to 510 mm, preferably 505 mm. Silicon based oil such as Poly Dimethylsiloxane (PDMS) is used as the oil 33. Preferably, the oil 33 has viscosity of 300 cs at a room temperature, and has a filling level of 340 cc to 360 cc, preferably 350 cc. It is to be understood that the present invention is not limited to the aforementioned characteristic values of the balancer.

Hereinafter, a method of using movement of the ball inside the balancer when the drum is rotated with unbalance will be described. Since the balancer is mounted on the drum and then rotated together with the drum, movement of the ball inside the balancer can be controlled finally by rotation control of the drum.

In particular, if the rotation speed of the drum is close to natural vibration of the laundry machine, the vibration of the drum may occur seriously. In this case, it is important how the ball is controlled.

In the laundry machine according to the related art, a natural vibration mode occurs in the range of 200 rpm to 270 rpm. Such a period where the natural vibration mode occurs may be referred to as a transient region. In this transient region, a plurality of natural vibration modes may exist. If the drum should be rotated at a rotation speed more than the transient region, it is important to control the ball such that the vibration of the drum becomes low.

FIG. 7 illustrates a graph showing a relation of mass vs. a natural frequency. It is assumed that, in vibration systems of two laundry machines, the two laundry machines have mass of m0 and m1 respectively and maximum holding laundry amounts are Δm, respectively. Then, the transition regions of the two laundry machines can be determined taking Δnf0 and Δnf1 into account, respectively. In this instance, amounts of water contained in the laundry will not be taken into account, for the time being.

In the meantime, referring to FIG. 7, the laundry machine with smaller mass m1 has a range of the transition region greater than the laundry machine with greater mass m0. That is, the range of the transition region having variation of the laundry amount taken into account becomes the greater as the mass of the vibration system becomes the smaller.

The ranges of the transition regions will be reviewed on the related art laundry machine and the laundry machine of the embodiment.

The related art laundry machine has a structure in which vibration is transmitted from the drum to the tub as it is, causing the tub to vibrate. Therefore, in taking the vibration of the related art laundry machine into account, the tub is indispensible. However, in general, the tub has, not only a weight of its own, but also substantial weights at a front, a rear or a circumferential surface thereof for balancing. Accordingly, the related art laundry machine has great mass of the vibration system.

Opposite to this, in the laundry machine of the embodiment, since the tub, not only has no weight, but also is separated from the drum in view of a supporting structure, the tub may not be put into account in consideration of the vibration of the drum. Therefore, the laundry machine of the embodiment may have relatively small mass of the vibration system.

Then, referring to FIG. 7, the related art laundry machine has mass m0 and the laundry machine of the embodiment has mass m1, leading the laundry machine of the embodiment to have a greater transition region, at the end.

Moreover, if the amounts of water contained in the laundry are taken into account simply, Δm in FIG. 7 will become greater, making a range difference of the transition regions even greater. And, since, in the related art laundry machine, the water drops into the tub from the drum even if the water escapes from the laundry as the drum rotates, an amount of water mass reduction come from the spinning is small. Since the laundry machine of the embodiment has the tub and the drum separated from each other in view of vibration, the water escaped from the drum influences the vibration of the drum, instantly. That is, the influence of a mass change of the water in the laundry is greater in the laundry machine of the embodiment than the related art laundry machine.

Under above reason, though the related art laundry machine has the transition region of about 200-270 rpm, A start RPM of the transient region of the laundry machine according to this embodiment may be similar to a start RPM of the transient region of the conventional laundry machine. An end RPM of the transient region of the laundry machine according to this embodiment may increase more than a RPM calculated by adding a value of approximately 30 % of the start RPM to the start RPM. For example, the transient region finishes at an RPM calculated by adding a value of approximately 80 % of the start RPM to the start RPM. According to this embodiment, the transient region may include a RPM band of approximately 200 to 350 rpm.

In the meantime, by reducing intensity of the vibration of the drum, unbalance may be reduced. For this, even laundry spreading is performed for spreading the laundry in the drum as far as possible before the rotation speed of the drum enters into the transition region.

In a case, a balancer is used, a method may be put into account, in which the rotation speed of the drum passes through the transition region while movable bodies provided in the balancer are positioned on an opposite side of an unbalance of the laundry. In this instance, it is preferable that the movable bodies are positioned at exact opposite of the unbalance in middle of the transition region.

However, as described above, the transient region of the laundry machine according to this embodiment is relatively wide in comparison to that of the conventional laundry machine. Because of that, even if the laundry even-spreading step or ball balancing is implemented in a RPM band lower than the transient region, the laundry might be in disorder or balancing might be failed with the drum speed passing the transient region.

As a result, balancing may be implemented at least one time in the laundry machine according to this embodiment before and while the drum speed passing the transient region. Here, the balancing may be defined as rotation of the drum at a constant-speed for a predetermined time period. Such the balancing allows the movable body of the balancer to the opposite positions of the laundry, only to reduce the unbalance amount. By extension, the effect of the laundry even-spreading. Eventually, the balancing is implemented while the drum speed passing the transient region and the noise and vibration generated by the expansion of the transient region may be prevented.

Here, when the balancing is implemented before the drum speed passing the transient region, the balancing may be implemented in a different RPM band from the RPM of the conventional laundry machine. For example, if the transient region starts at 200 RPM, the balancing is implemented in the RPM band lower than approximately 150 RPM. Since the conventional laundry machine has a relatively less wide transient region, it is not so difficult for the drum speed to pass the transient region even with the balancing implemented at the RPM lower than approximately 150 RPM. However, the laundry machine according to this embodiment has the relatively wide expanded transient region as described above. if the balancing is implemented at the such the low RPM like in the conventional laundry machine, the positions of the movable bodies might be in disorder by the balancing implemented with the drum speed passing the transient region. Because of that, the laundry machine according to this embodiment may increase the balancing RPM in comparison to the conventional balancing RPM, when the balancing is implemented before the drum speed enters the transient region. That is, if the start RPM of the transient region is determined, the balancing is implemented in a RPM band higher than a RPM calculated by subtracting a value of approximately 25 % of the start RPM from the start RPM. For example, the start RPM of the transient region is approximately 200 RPM, the balancing may be implemented in a RPM band higher than 150 RPm lower than 200 RPM.

Moreover, the unbalance amount may be measured during the balancing. That is, the control method may further include a step to measure the unbalance amount during the balancing and to compare the measured unbalance amount with an allowable unbalance amount allowing the acceleration of the drum speed. If the measured unbalance amount is less than the allowable unbalance amount, the drum speed is accelerated after the balancing to be out of the transient region. In contrast, if the measured unbalance amount is the allowable unbalance amount or more, the laundry even-spreading step may be re-implemented, in this case, the allowable unbalance amount may be different from an allowable unbalance amount allowing the initial accelerating.

Generally, the transient region may be defined as a rotation speed range of the drum. As described above, the transient region may be defined as a region that includes natural vibration. In the vibration system, natural vibration is determined by mass and rigidity (for example, spring constant). Since mass may be varied depending on the amount of laundry in the laundry machine, the transient region is preferably controlled considering mass.

In order to reduce the vibration of the drum at the transient region, the unbalance rate may be reduced. In this case, uniform laundry distribution for uniformly distributing the laundry inside the drum is carried out before the rotation speed of the drum enters the transient region.

If the balancer is used, the rotation speed of the drum may quickly pass through the transient region while the balls are being located at an opposite position of the unbalanced position of the laundry. At this time, in the middle of the transient region, the balls are preferably located at the opposite position of the unbalanced position. In this case, the relation between the position of the balls and the unbalanced position can be defined by an angle (hereinafter, referred to as ‘nearest ball angle’) of the ball located nearest to unbalance with respect to the centrifugal force center of the unbalance.

FIG. 4 illustrates the position relation between unbalance (UB) and the balls. In FIG. 4, the position relation between the balls and unbalance illustrate that the nearest ball angle is θ1 and a centrifugal force center angle is θ2. For convenience' sake, the angle between the ball and unbalance will mean θ1 or θ2.

A steel ball can be used as the ball. If the sizes of the balls are uniformly provided and the balls are arranged in parallel to adjoin one another, the centrifugal force center is P1 as shown in FIG. 4.

The ball is rotated by a friction force generated when the drum is rotated. When the drum is rotated, the ball is not kept in the drum and it is rotated at a different speed from that of the drum. Here, unbalance means the laundry being in close contact with an inner wall of the drum and it can be rotated at almost the same speed as that of the drum because of an enough friction force and the lift of the inner wall. As a result, the rotation speed of the unbalance is different from that of the ball. Since the balls are rotated by rotation of the drum, the rotation speed of the unbalance is faster than that of the balls. Precisely, an angular velocity of the unbalance is faster than that of the balls.

If the rotation speed of the drum is getting faster, the balls will be in close contact with an outer circumferential surface of the ball space portion of the racer because of a centrifugal force. If the friction force between the circumferential surface and the balls is a predetermined value or more, the balls will be rotated with the same rotation speed as that of the drum. In this case, the balls are located at a predetermined position with respect to the drum in the same manner as the unbalance. In this specification, the case of the ball being rotated at the predetermined position with respect to the drum will be referenced to as ‘balancing position’ or ‘balancing’ for convenience' sake.

For the ball balanced rotation speed, the minimum rotation speed may be varied depending on the balancer. Also, the minimum rotation speed may be varied depending on whether the balancer is installed perpendicularly or horizontally. If the balancer is installed perpendicularly, the positions of the balls being in contact with the outer circumferential surface of the ball space portion of the race may be varied by gravity. The balls maintained at constant speed rotation of the ball balanced rotation speed may be located at the opposite position of the unbalanced position. Referring to FIG. 4, the balls may be located at P2.

In the mean time, balancing may not be carried out at a rotation speed lower than the transient region due to a low centrifugal force. Accordingly, when the rotation speed of the drum passes through the transient region, instead of carrying out balancing, the position of the balls is checked while the drum is being rotated at a constant speed, whereby the balls can be located at the opposite position of the unbalanced position when the rotation speed of the drum passes through the transient region. In other words, even though balancing is not carried out, it can be controlled such that the rotation speed of the drum passes through the transient region while the balls are being located at the opposite position of the unbalanced position. For example, referring to FIG. 4, it can be controlled such that the rotation speed of the drum passes through the transient region when the angle θ1 or θ2 between the ball and unbalance is more than 90°. At this time, in the middle of the transient region, it may be preferable that the angle is 180°.

When the drum is rotated at a constant speed more than the transient region as above, the vibration of the drum may occur such that displacement at the front portion of the drum is equal to that at the rear portion of the drum. Accordingly, as shown in FIG. 5, an angle θ3 between the front balls 32 f and the rear balls 32 e may be within 90°. FIG. 5 is a diagram illustrating the position relation between the front balls 32 f and the rear balls 32 e when viewed through the drum in a forward direction.

At the transient region, a vibration mode where front displacement of the vibration of the drum is different from rear displacement thereof may occur. For example, a vibration mode where front displacement of the vibration of the drum is opposite to rear displacement thereof may occur. For convenience' sake, this vibration mode will be referred to as a diagonal vibration mode. Meanwhile, the transient region of the laundry machine of this embodiment may expand compared to the conventional laundry machine. Therefore, the vibration mode of the drum may be changed due to the expanded transient region, for example, the diagonal vibration mode can be generated. In this diagonal vibration mode, if the rear balls 32 f and the rear balls 32 e are maintained at an angle within the range of 90° as described above, unbalance to the diagonal vibration mode may not be compensated normally, whereby the vibration of the drum may become severe.

The aforementioned diagonal vibration mode may start to occur as the vibration of the drum becomes close to natural vibration of the natural vibration mode corresponding to the diagonal vibration mode.

Accordingly, in order to reduce the vibration of the drum, the positions of the front balls 32 f and the rear balls 32 e should be corrected before the vibration of the drum reaches the natural vibration of the diagonal vibration mode.

To this end, before the vibration of the drum reaches the natural vibration, the drum is preferably subjected to constant speed rotation for a predetermined time at a rotation speed where the diagonal vibration mode occurs, whereby the positions of the front balls 32 f and the rear balls 32 e are corrected to compensate for unbalance.

In particular, the aforementioned laundry machine of this embodiment has a different structure from that of the related art. Since the natural vibration mode corresponding to the diagonal vibration mode may occur at the transient region, it is preferably required to correct the positions of the balls as described above.

Hereinafter, a control method for passing through the transient region to carry out a spinning cycle in the aforementioned laundry machine will be described using a rotation speed graph of the drum based on the passage of time with reference to FIG. 6. In FIG. 6, period ‘a’ denotes a first constant speed rotation step, period ‘b’ a second constant speed rotation step, period ‘c1’ a first transient region step, period ‘c2’ third constant speed rotation step, period ‘c3’ a second transient region step, and period ‘d’ fourth constant speed rotation step.

First of all, at the period ‘a’, laundry distribution or laundry disentangling is carried out, and a first unbalance value is sensed while the drum is rotated at a constant speed of a first rotation speed, and then the sensed first unbalance value is compared with a first allowable unbalance value.

At this time, if the sensed first unbalance value is less than the first allowable unbalance value, the drum is accelerated to reach a second rotation speed and then rotated at a constant speed (period ‘b’). At the period ‘b’, a second unbalance value is sensed and then the sensed second unbalance value is compared with a second allowable unbalance value. If the sensed second unbalance value is less than the second allowable unbalance value, the drum is subjected to warming-up for passing through the transient region period ‘c’.

In this case, as shown in A of FIG. 6, at the first transient region period ‘c1’, the natural vibration mode where vibration displacement at the front portion of the drum is equal to that at the rear portion of the drum occurs. As shown in B of FIG. 6, at the second transient region period ‘c3’ the natural vibration mode corresponding to the diagonal vibration mode where vibration displacement at the front portion of the drum is contrary to that at the rear portion of the drum occurs.

First of all, in order to pass through the period ‘c1’the drum is rotated at a constant speed at the period ‘b’ to check the position of the ball, whereby an acceleration timing t1 is determined. At the period ‘c1’, t1 and its acceleration inclination are determined such that the angle between the unbalance and the ball is in the range of 90° or more. At this time, in the middle of the period ‘c1’, t1 and its acceleration inclination can be determined such that the angle between the unbalance and the ball is in the range of 180°. At the period ‘c1’, the centrifugal force center of the front balls 32 f and the centrifugal force center of the rear balls 32 e can define an angle within the range of 90° based on the rotation center of the drum when viewed in a forward direction. Preferably, the front balls 32 f and the rear balls 32 e are located within the range of 90° to reduce the vibration of the vibration mode where displacement at the front portion of the drum and displacement at the rear portion of the drum are equal to each other in a perpendicular direction with respect to the rotational shaft.

If the rotation speed of the drum reaches the third rotation speed via the period ‘c1’, the drum is rotated at a constant speed for a predetermined time (period ‘c2’). The period ‘c2’may be regarded as a warming-up period for passing through the natural vibration mode corresponding to diagonal vibration that may occur at the period ‘c3’. At the period ‘c2’, the drum may be vibrated in the diagonal vibration mode as it is rotated at a rotation speed near the natural vibration of the natural vibration mode corresponding to the diagonal vibration. At this time, as the drum is rotated at a constant speed for a predetermined time, the position of the balls of the front balancer and the rear balancer is varied depending on the corresponding vibration mode.

After passing through the period ‘c2’, the rotation speed of the drum passes through the transient region at the period ‘c3’ in a state that the angle between the front balls 32 f and the front unbalance and the angle between the rear balls 32 e and the rear unbalance are 90° or more, respectively. At this time, when viewed from the drum in a forward direction, the angle between the front balls 32 f and the rear balls 32 e may be 90° or more. In order to reduce vibration of the diagonal vibration mode, it is preferable that the angle between the front balls 32 f and the rear balls 32 e is 90° or more.

The third rotation speed and the predetermined time can be determined considering that the front balancer and the rear balancer are subjected to balancing. In other words, as the drum is rotated at the third rotation speed for the predetermined time, the third rotation speed and the predetermined time can be determined in such a manner that the front balls 32 f and the rear balls 32 e are moved to a position for compensating front unbalance and a position for compensating rear unbalance, respectively, at angles of 180°, respectively, and then are maintained at their positions, respectively.

In this embodiment, the third rotation speed is preferably set in the range of 250 rpm to 290 rpm. If the rotation speed of the drum is too low, a vibration level of the diagonal vibration mode becomes weak, whereby the period ‘c2’ becomes longer or balancing may not be carried out preferably. Also, if the rotation speed of the drum is too high, severe vibration occurs and movement of the balls becomes unstable, whereby the positions of the balls may not be varied normally. Preferably, the third rotation speed of the drum is set in the range of 270 rpm. The period ‘c2’ is preferably maintained for 30 seconds, approximately.

The rotations speed of the drum strays from the transient region while it is passing through the period ‘c3’ where the natural vibration mode corresponding to diagonal vibration occurs. Afterwards, the rotation speed of the drum enters the period for rotating the drum at high speed to carry out the spinning cycle. At this time, it is necessary to vary the positions of the balls before the rotation speed of the drum enters the main spinning step.

At the period ‘c2’, since the front balls and the rear balls are located to be suitable for compensating the unbalance to diagonal vibration, they may not be suitable for the main spinning step having a vibration mode different from the diagonal vibration mode.

Accordingly, the period ‘d’ for realigning the positions of the balls while the rotation speed of the drum is maintained at a constant speed rotation of a fourth rotation speed after passing through the transient region will be required. In other words, it is preferably required to realign the balls to be suitable for compensating the unbalance to the vibration mode of the main spinning step.

As the balls are moved at the main spinning step, unbalance may occur severely. Accordingly, balancing is preferably carried out at the period ‘d’. In other words, the rotation speed of the drum is preferably maintained at the fourth rotation speed suitable for the corresponding vibration mode such that the balls are located to compensate for unbalance.

The fourth rotation speed is preferably determined at a rotation speed that does not allow the diagonal vibration mode if possible. For example, the fourth rotation speed is preferably determined at a rotation speed different from the natural vibration of the diagonal vibration mode as much as a predetermined rate, whereby the fourth rotation speed is not affected by the diagonal vibration mode.

At the period ‘d’ the rotation speed of the drum can maintained in the range of 370 rpm to 390 rpm for 50 seconds to 70 seconds, preferably 60 seconds.

In the mean time, it is preferable that the acceleration inclination at the period ‘c1’ is smaller than that at the period ‘c3’. If the balancing is carried out at the third rotation speed, since the balls may little be moved, the rotation speed of the drum can quickly pass through the period ‘c3’. However, the balls continue to move without being balanced at the period ‘cl’ and considering such a movement of the balls, the rotation speed for passing through the period ‘cl’ is determined.

Finally, after passing through the period ‘d’ the main spinning step is carried out at 1000 rpm or more to spin the laundry.

Although the spinning cycle is carried out for example in this embodiment, this embodiment may be applied to any other case where the drum is rotated at a speed more than the transient region.

First, vibration characteristics of the laundry machine according to the embodiment of the present invention will now be described with reference to FIG. 8.

As the rotation speed of the drum is increased, a region (hereinafter, referred to as“transient vibration region”) where irregular transient vibration with high amplitude occurs is generated. The transient vibration region irregularly occurs with high amplitude before vibration is transited to a steady-state vibration region (hereinafter, referred to as“steady-state region”), and has vibration characteristics determined if a vibration system (laundry machine) is designed. Though the transient vibration region is different according to the type of the laundry machine, transient vibration occurs approximately in the range of 200 rpm to 270 rpm. It is regarded that transient vibration is caused by resonance. Accordingly, it is necessary to design the balancer by considering effective balancing at the transient vibration region.

In the mean time, as described above, in the laundry machine according to the embodiment of the present invention, the vibration source, i.e., the motor and the drum connected with the motor are connected with the tub 12 through the rear gasket 250. Accordingly, vibration occurring in the drum is little forwarded to the tub, and the drum is supported by a damping means and the suspension unit 180 via a bearing housing 400. As a result, the tub 12 can directly be fixed to a cabinet 110 without any damping means.

As a result of studies of the inventor of the present invention, vibration characteristics not observed generally have been found in the laundry machine according to the present invention. According to the general laundry machine, vibration (displacement) becomes steady after passing through the transient vibration region. However, in the laundry machine according to the embodiment of the present invention, a region (hereinafter, referred to as“irregular vibration”) where vibration becomes steady after passing through the transient vibration region and again becomes great may be generated. For example, if the maximum drum displacement or more generated in an RPM band lower than the transient region or the maximum drum displacement or more of steady state step in a RPM band higher than the transient region is generated, it is determined that irregular vibration is generated. Alternatively, if an average drum displacement in the transient region, +20 % to −20 % of the average drum displacement in the transient region or ⅓ or more of the maximum drum displacement in the natural frequency of the transient region are generated, it may be determined that the irregular vibration is generated.

However, as a result of the studies, irregular vibration has occurred in a RPM band higher than the transient region, for example has occurred at a region (hereinafter, referred to as“irregular vibration region”) in the range of 350 rpm to 1000 rpm, approximately. Irregular vibration may be generated due to use of the balancer, the damping system, and the rear gasket. Accordingly, in this laundry machine, it is necessary to design the balancer by considering the irregular vibration region as well as the transient vibration region.

For example, the balancer is provide with a ball balancer, it is preferable that the structure of the balancer, i.e., the size of the ball, the number of balls, a shape of the race, viscosity of oil, and a filling level of oil are selected by considering the irregular vibration region as well as the transient vibration region. When considering the transient vibration region and/or the irregular vibration region, especially considering the irregular vibration region, the ball balancer has a greater diameter of 255.8 mm and a smaller diameter of 249.2. A space of the race, in which the ball is contained, has a sectional area of 411.93 mm ². The number of balls is 14 at the front and the rear, respectively, and the ball has a size of 19.05 mm. Silicon based oil such as Poly Dimethylsiloxane (PDMS) is used as the oil. Preferably, oil has viscosity of 300 CS at a room temperature, and has a filling level of 350 cc.

In addition to the structure of the balancer, in view of control, it is preferable that the irregular vibration region as well as the transient vibration region is considered. For example, to prevent the irregular vibration, if the irregular vibration region is determined, the balancing may be implemented at least one time before, while and after the drum speed passes the irregular vibration region. Here, if the rotation speed of the drum is relatively high, the balancing of the balancer may not be implemented properly and the balancing may be implemented with decreasing the rotation speed of the drum, however, if the rotation speed of the drum is decreased to be lower than the transient region to implement the balancing, it has to pass the transient region again. In decreasing the rotation speed of the drum to implement the balancing, the decreased rotation speed may be higher than the transient region.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

1. A control method of laundry machine having a drum, a front balancer provided with a front portion of the drum and a rear balancer provided with a rear portion of the drum, the control method comprising: accelerating the drum and rotating the drum at a constant speed of a predetermined rotation speed for a predetermined time period, the predetermined rotation speed allowing that perpendicular displacement at the front portion of the drum is different from that at the rear portion of the drum.
 2. The control method as claimed in claim 1, wherein the predetermined rotation speed is included in the transient region.
 3. The control method as claimed in claim 1, wherein perpendicular displacement at the front portion of the drum with respect to a rotational shaft of a transient region is contrary to that at the rear portion of the drum at the predetermined rotation speed.
 4. The control method as claimed in claim 1, wherein the control method further comprising: a first transient region step for entering a transient region by accelerating the drum; a third constant speed rotation step for rotating the drum at a constant speed of a third rotation speed for a first predetermined time, the third rotation speed allowing that perpendicular displacement at the front portion of the drum with respect to a rotational shaft of the transient region is contrary to that at the rear portion of the drum; and a second transient region step for straying from the transient region by accelerating the drum at the third rotation speed or more.
 5. The control method as claimed in claim 4, wherein the second transient region step includes a rotation speed allowing a natural vibration mode where perpendicular displacement to the rotational shaft of the drum at the front portion of the drum is contrary to that at the rear portion of the drum.
 6. The control method as claimed in claim 5, wherein the first predetermined time of the third constant speed rotation step is determined such that an angle between the front balls and front unbalance of the drum is 90° or more and an angle between the rear balls and rear unbalance of the drum is 90° or more.
 7. The control method as claimed in claim 6, wherein the first predetermined time of the third constant speed rotation step is determined such that an angle between a centrifugal force center of the front balls and the front unbalance is 180° and an angle between a centrifugal force center of the rear balls and the rear unbalance is 180°.
 8. The control method as claimed in claim 7, wherein the first predetermined time of the third constant speed rotation step is determined such that the angle between the centrifugal force center of the front balls and the front unbalance and the angle between a centrifugal force center of the rear balls and the rear unbalance are uniformly maintained, respectively.
 9. The control method as claimed in claim 6, wherein, at the second transient region step, an angle between the centrifugal force center of the front balls and the centrifugal force center of the rear balls is 90° or more when viewed at the front portion of the drum.
 10. The control method as claimed in claim 6, wherein the third rotation speed of the third constant speed rotation step is maintained in the range of 250 rpm to 290 rpm.
 11. The control method as claimed in claim 10, wherein the third rotation speed of the third constant speed rotation step is maintained at 270 rpm.
 12. The control method as claimed in claim 6, wherein the third rotation speed allows the front balancer and the rear balancer to be subjected to balancing.
 13. The control method as claimed in claim 12, wherein the second transient region step has an acceleration inclination greater than that of the first transient region step.
 14. The control method as claimed in claim 4, further comprising the step of a fourth constant speed rotation step for rotating the drum at a constant speed of a fourth rotation speed for a second predetermined time after the second transient region step.
 15. The control method as claimed in claim 14, wherein the fourth rotation speed allows the drum to be vibrated such that perpendicular displacement to the rotational shaft of the drum at the front portion of the drum is equal to that at the rear portion of the drum.
 16. The control method as claimed in claim 4, wherein the first transient region step includes a rotation speed allowing a natural vibration mode where perpendicular displacement to the rotational shaft of the drum at the front portion of the drum is equal to that at the rear portion of the drum.
 17. The control method as claimed in claim 16, wherein, at the first transient region step, an angle between the centrifugal force center of the front balls and the centrifugal force center of the rear balls is within 90° when viewed at the front portion of the drum.
 18. The control method as claimed in claim 4, further comprising: a first constant speed rotation step for rotating the drum at a constant speed of a first rotation speed, sensing a first unbalance, and comparing the sensed first unbalance with a first allowable unbalance; and a second constant speed rotation step for sensing a second unbalance at a second rotation speed of the drum greater than the first rotation speed and comparing the sensed second balance with a second allowable balance.
 19. A control method of a laundry machine having a drum, a front balancer provided with a front portion of the drum, and a rear balancer provided with a rear portions of the drum, the control method comprising: a first transient region step for passing through a rotation speed allowing a natural vibration mode where perpendicular displacement to a rotational shaft of the drum at the front portion of the drum is equal to that at the rear portion of the drum; a constant speed rotation step for rotating the drum at a constant speed for a predetermined time after the first transient region step; and a second transient region step for passing through a rotation speed allowing a natural vibration mode where perpendicular displacement to a rotational shaft of the drum at the front portion of the drum is contrary to that at the rear portion of the drum.
 20. The control method as claimed in claim 1, wherein the laundry machine comprises a driving unit comprising a shaft connected to a drum, a bearing housing to rotatably support the shaft, and a motor to rotate the shaft, and a suspension assembly is connected to the driving unit.
 21. The control method as claimed in claim 1, wherein the laundry machine comprises a rear gasket for sealing to prevent washing water from leaking from a space between a driving unit and a tub, and enabling the driving unit movable relative to the tub.
 22. The control method as claimed in claim 1, wherein a tub is supported rigidly more than a drum being supported by a suspension assembly.
 23. The control method as claimed in claims 20, wherein the front balancer and the rear balancer have 14 balls, respectively, each of the balls has a diameter of 18.55 mm to 19.55 mm, a race for receiving the balls includes a ball space portion having a sectional area in the range of 410 mm ² to 413 mm ², and a center diameter of the sectional area of the ball space portion is in the range of 500 mm to 510 mm.
 24. The control method as claimed in claim 20, wherein each of the ball space portions of the front balancer and the rear balancer is filled with oil having viscosity of 300 cs at a filling level of 340 cc to 360 cc.
 25. The control method as claimed in claim 7, wherein the third rotation speed of the third constant speed rotation step is maintained in the range of 250 rpm to 290 rpm.
 26. The control method as claimed in claim 8, wherein the third rotation speed of the third constant speed rotation step is maintained in the range of 250 rpm to 290 rpm.
 27. The control method as claimed in claim 9, wherein the third rotation speed of the third constant speed rotation step is maintained in the range of 250 rpm to 290 rpm.
 28. The control method as claimed in claim 7, wherein the third rotation speed allows the front balancer and the rear balancer to be subjected to balancing.
 29. The control method as claimed in claim 8, wherein the third rotation speed allows the front balancer and the rear balancer to be subjected to balancing.
 30. The control method as claimed in claim 9, wherein the third rotation speed allows the front balancer and the rear balancer to be subjected to balancing.
 31. The control method as claimed in claim 21, wherein the front balancer and the rear balancer have 14 balls, respectively, each of the balls has a diameter of 18.55 mm to 19.55 mm, a race for receiving the balls includes a ball space portion having a sectional area in the range of 410 mm ² to 413 mm ², and a center diameter of the sectional area of the ball space portion is in the range of 500 mm to 510 mm.
 32. The control method as claimed in claim 22, wherein the front balancer and the rear balancer have 14 balls, respectively, each of the balls has a diameter of 18.55 mm to 19.55 mm, a race for receiving the balls includes a ball space portion having a sectional area in the range of 410 mm ² to 413 mm ², and a center diameter of the sectional area of the ball space portion is in the range of 500 mm to 510 mm.
 33. The control method as claimed in claim 21, wherein each of the ball space portions of the front balancer and the rear balancer is filled with oil having viscosity of 300 cs at a filling level of 340 cc to 360 cc.
 34. The control method as claimed in claim 22, wherein each of the ball space portions of the front balancer and the rear balancer is filled with oil having viscosity of 300 cs at a filling level of 340 cc to 360 cc. 